Such networks are also dubbed Wi-Fi networks. They are used, in numerous applications, to network stations (for example computers, personal assistants and peripherals).
The 802.11 standard defines in the document “IEEE 802.11a-1999, IEEE 802.11b-1999, IEEE-802.11d-2001, Part 11: wireless LAN medium access control (MAC) and physical layer (PHY) specifications” a method for regulating the traffic in the wireless network. This method uses a system of congestion windows (Congestion Window “CW”) to regulate this traffic. According to this standard, to determine the instant at which to send a data packet, a station draws a random number between 0 and CW−1, the value CW being an integer lying between two values CWmin and CWmax specified by the 802.11 standard.
This value CW serves as backward counter for the sending of the packet, this counter being deferred if the station finds that another station is currently sending. Unfortunately, this congestion windows system generates a significant number of collisions on the wireless network, thereby resulting, from the user's point of view, in a significant loss of bandwidth.
Another mechanism known by the name “tournament scheme” may be used by the various stations to regulate packet sending and limit the collision rate. This tournament scheme is described in the document by the authors Z. Abichar and M. Chang, entitled “CONTI: Constant Time Contention Resolution for WLAN Access”, IFIP Networking 2005.
The tournament scheme consists in organizing a sort of tournament between the stations having to send a packet. A tournament is composed of a certain number of selection rounds, each executed for a time interval of predefined duration allowing each station to have time to hear the sending of any other. This duration can typically be equal to the duration of the time interval dubbed the “SlotTime” which, according to the IEEE 802.11 standard, is defined as elementary interval in the contention resolution procedure based on congestion windows. At the start of the tournament, all the stations having to send a packet may be permitted to send this packet. At each selection round, one or more stations may be deleted from the list of stations permitted to send, depending on whether a permission or a prohibition to send is allotted to them during this selection round. On completion of the tournament, only the non-eliminated stations are permitted to send. If several stations are still in the running on completion of the tournament, they send at the same time thus causing a collision and therefore disturbed reception with the impossibility of correctly receiving the data packets sent. These stations will then have to participate in the next tournament to attempt to send these packets again.
In the case of the sending of data streams requiring priority access to the network or a high bandwidth, the requirement is apparent to provide a solution for regulating sending making it possible to guarantee a level of performance in terms of bandwidth or throughput as well as a quality of service.
The current solution, compatible with the IEEE 802.11e standard, consists in increasing the probability that a priority stream accesses the radio medium before the others. Now, this simplistic solution does not make it possible to guarantee that a station having to send a priority stream accesses the radio medium in a predefined time, or that sufficient bandwidth is at its disposal. Furthermore, this solution does not make it possible to guarantee a minimum level of performance to the other stations having to send streams of lower priority, since no measure is taken for these other stations.
There is therefore no equitable mechanism for sharing access to the network between various user stations which are usable with the mode of access according to the 802.11e standard or the mode of access according to the tournament scheme.